Stray light and lens flare, what are they? These effects can occur when one or several sources of light shine directly at the front lens of the lens, generally it is direct sunlight. Example images are further below in the article. Depending on the lens’s design and quality and the filter used, lens flare or a reduction in contrast due to stray light can be more or less pronounced. The shape of the lens flare reflections depends on the shape of the diaphragm. In contrast to stray light, lens flares are not always disruptive to an image; they can be used intentionally to create certain images (see below). There are effect filters in image processing that artificially create this effect.

Lens hoods not only reduce the effects mentioned above, but they also provide additional protection for the front lens or the built in filter. There is no reason why you should not always leave the lens flare on the lens, unless you are capturing images with a built-in flash or a flash attachment. In images captured using flash lens flares can cast an undesirable shadow. Some lens flares, therefore, have an opening that can be closed on their upper side, which allows the use of built-in flashes.
It is recommendable to use specially manufactured lens flares that fit the lens to ensure optimal impact. If a lens flare is not adjusted to the lens’s focal lengths, it can result in unwanted shadows on the edges of the photos. This is also called mechanical vignetting. Lens flares on zoom lenses need to be adjusted to shorter focal lengths. In the case of telephoto focal lengths, they do not provide the maximum possible protection of the front lens against backlighting and side lighting.

Images one and two show kidney-shaped lens flares by the company Nikon. They are specially manufactured for each individual lens and provide maximum effect.
These two models are different in length. This difference is due to the different focal lengths of the lens. The longer the focal length is, the longer the lens flare can be without it casting a shadow (vignetting) on the edges of the image. Image three shows an enclosed design (not kidney-shaped) of a lens flare, which is used mostly for telephoto lenses. It is also used on lens without a built-in focus.

There are various ways to attach lens hoods to lenses. Most models are attached to the lens using a bayonet mount. Older models were usually screwed directly onto the filter thread.

Example images for lens flare and stray light
In the following image you can see the lens flare clearly that was caused by the sunlight directly hitting the front lens. In this case, it was intentional to create this effect and no lens hood was used. The image illustrates that lens flare can have a positive effect in an image. However, these lens flares often become a disruptive element, especially when they hide important image details. In using a lens hood, the lens flare could have been avoided as the sun had not hit image section.

Lens flare – Sunrise in the Bavarian Prealps

In the following image, there is also lens flare to be seen. However, here the lens flare could not have been avoided by using a lens hood as the light source (sun) was shining directly at the image section.

Lens flare – Sunset in autumnal Spessart

Both of the following images can be seen in quick succession. Look at the difference in contrast. The somewhat brighter, less contrasted image was captured without a lens hood.

Stray light – Sunrise in the Bavarian Prealps

Reduction of stray light and lens flare without a lens hood
Trees, houses or other objects can replace a lens hood, if need be, if you are in the shade holding the camera, i.e., the front lens is the object’s shadow. You can also take advantage of clouds blocking the sun. Often you can use your hand to provide some shade. Unfortunately, the camera can often not be held as steadily with just one hand, which can result in blurring or problems in the image build-up. Especially when using heavy telephoto lens, it is often impossible to hold the camera in one hand due to its weight. Congratulations to anyone who has the fitting lens hood to hand.